1. Field of the Invention
This invention relates to an exercise device utilizing a resistance element for development of muscular strength, size and endurance.
2. Description of Background and Relevant Information
Exercise devices for muscular strength training typically employ resistance elements utilizing a gravitational mass or resilient materials. Exercise devices utilizing a gravitational mass resistance element exhibit the highly desirable characteristic of providing a constant resistance force throughout the range of exercise movement. However, the high weight of a gravitational resistance element causes considerable difficulties in shipping and on site mobility of the exercise device. Resilience based exercise machines such as the Bowflex™ (U.S. Pat. No. 4,620,704) and Soloflex™ (U.S. Pat. No. 4,587,320) therefore dominate the direct sales market.
Exercise devices based on resilient materials, although light, suffer from the problem of a varying resistance force. Resistance increases progressively during the exercise stroke as the elongation or compression of the resilient medium increases. A resistance too low for maximal muscular development occurs over most of the exercise stroke. Designs to convert a resilient resistance to constant force are often complicated (U.S. Pat. No 5,382,212). Other designs fail to adequately deal with the large ratio of force possible with a resilient element with zero initial resistance.
Adjustment of the exercise force is a crucial factor in the success of strength training devices. Resistance should be adjustable to accommodate different exercises and users. Users also need to increase resistance over time for an exercise movement as strength develops. Most resilient exercise machines, such as the Bowflex™ and Soloflex™, allow resistance to be changed by selectively engaging different resistance elements, or by adding resistance elements in parallel. Adjusting resistance in this way is time consuming and only permits resistance changes in fixed increments, usually 5 lbs at a time. Tension must be removed from the resistance elements to effect the change, so the exercise stroke begins at a minimal resistance level.
Another method of adjusting resistance of a resilient resistance involves varying the force attachment point along a lever arm (U.S. Pat. No. 3,638,941). Lever arm arrangements suffer from a few problems. First, the lever arm modifies the input resistance force according to a cosine function. This results in greatest force transmission when the level position is perpendicular to the input force, and lower forces elsewhere along the arc of the lever arm. Second, lever arms are not space efficient.
An exercise device that solves these problems efficiently could be produced at lower cost, allowing more consumers to experience the benefits of strength training and muscular development. An easy to use mechanism for adjusting resistance force can reduce workout times and increase opportunities for strength progression. Constant force allows a user to perform more exercise work during a stroke.